A hot runner valve gate stem is usually guided in a bushing as it passes through the hot runner manifold or the nozzle housing. However, plastic leakage at this point represents a serious problem. In some cases drool channels are provided to allow the plastic leakage to escape.
U.S. Pat. No. 4,268,240 to Rees et al. shows a valve gate with a valve stem or rod and represents an early example of a valve gate where the valve stem is guided at the tip end. U.S. Pat. No. 3,677,682 to Putkowski shows a front mounted valve gate wherein the valve stem is operated by an external cylindrical piston surrounding the heated nozzle housing. U.S. Pat. No. 5,533,882 to Gessner et al. shows a hot runner valve gated system wherein a nozzle housing is positioned in a manifold plate and including a gate orifice and a reciprocal valve stem. U.S. Pat. No. 4,095,931 to Reitan shows a valve stem housed inside a torpedo containing a heater. The valve stem is guided and presumably seals at the tip, but heating the valve stem adjacent this so-called seal would be likely to promote leakage.
Prior art examples of guiding valve stems inside the nozzle housing are shown in the following U.S. Pat. Nos.: 4,412,807 to York; 4,712,995 to Basnett; 4,810,184 to Gellert et al.; 3,716,318 to Erik et al.; 4,925,384 to Manner; and 5,254,305 to Fernandez et al. However, these patents have no teaching for preventing leakage around the valve stem as it passes through the manifold or nozzle-bushing interface, which is a significant problem.
U.S. Pat. No. 4,430,258 to Gellert shows a bushing set in the nozzle casting for preventing leakage at the valve stem. U.S. Pat. No. 4,026,518 to Gellert shows a valve stem unit with a built in drainage channel to remove leakage around the valve stem at the bushing.
European Patent Application 0,405,007 to Gellert, published Jan. 2, 1991, shows a hot runner valve gate bushing having a single entry port that directs the melt flow to two opposing exit ports opening into the vale stem. The idea is to help avert the problem of the melt recombining lower down the valve stem which may cause flow lines in the final molded article. Similarly, U.S. Pat. Nos. 5,192,556 to Schmidt and 4,705,473 to Schmidt attempt to solve the same problem.
It is, therefore, a principal object of the present invention to provide an efficient and easy to use hot runner valve gate stem guide and seal.
It is a further object of the present invention to provide a device as aforesaid which minimizes or prevents leakage, which has been a significant problem heretofore.
Further objects and advantages of the present invention will appear hereinbelow.